The field of the invention relates to engine speed control in internal combustion engines.
A vehicle""s engine typically utilizes an idle speed control mode where engine speed is controlled to a desired speed when a vehicle is stationary or slowly moving and an operator is not requesting drive torque. During idle conditions, it is desirable to maintain a constant engine speed, thereby giving the operator superior drive feel. To keep engine speed constant, idle speed control should reject engine torque disturbances from various sources, such as, for example, air conditioning systems, power steering systems, changes in ambient conditions, or changes in any other devices that affect engine speed.
One method for controlling engine speed to a desired speed uses ignition timing, throttle position, or a combination of both. In one system a torque reserve is used so that it is possible to rapidly increase engine torque using ignition timing, thereby controlling engine speed. One example of a system using ignition timing is disclosed in U.S. Pat. No. 5,765,527.
The inventors herein have recognized several disadvantages with the above approaches. In particular, a disadvantage with using throttle position is that the throttle cannot quickly change engine torque since it controls flow entering an intake manifold. Controlling flow entering the manifold cannot rapidly control cylinder charge due to manifold volume. For example, if the throttle is instantly closed, cylinder air charge does not instantly decrease to zero. The engine must pump down the air stored in the manifold, which takes a certain number of revolutions. Therefore, the cylinder air charge gradually decreases toward zero.
Another disadvantage with the known approaches is related to ignition timing. In particular, to maximize fuel economy, ignition timing should be at MBT timing (ignition timing for maximum torque). However, when at MBT, adjustment of ignition timing in any direction decreases engine torque and fuel economy. Therefore, when maximizing fuel economy, load torques cannot be rejected since ignition timing can only decrease engine torque. To be able to use ignition timing in both positive and negative directions, ignition timing must be set away from MBT timing. This allows rapid engine torque control, but at the cost of degraded fuel economy.
An object of the present invention is to rapidly control engine speed to a desired engine speed while maximizing fuel economy.
The above object is achieved and disadvantages of prior approaches overcome by a method for controlling speed of an engine having at least one cylinder, the engine also having an intake manifold and an outlet control device for controlling flow from the intake manifold into the cylinder, comprising: generating a desired engine speed; and changing the outlet control device to control the engine speed to said desired engine speed.
By using an outlet control device that controls flow exiting the manifold (entering the cylinder), it is possible to rapidly change engine torque and engine speed, despite response delays of airflow inducted through the intake manifold. In other words, a rapid change in cylinder charge can be achieved, thereby allowing a rapid change in cylinder air/fuel ratio while preventing disturbances in engine torque.
An advantage of the above aspect of the invention is that engine speed can be more accurately controlled to a desired engine speed without fuel economy degradation.
In another aspect of the present invention, the above object is achieved and disadvantages of prior approaches overcome by a method for controlling speed of an engine having at least one cylinder, the engine also having an intake manifold and an outlet control device for controlling flow from the intake manifold into the cylinder and an inlet control device for controlling flow into the intake manifold, comprising: generating a desired engine speed; and changing both the outlet control device and the inlet control device based on the engine speed and said desired engine speed and in response to a respective outlet control device command and an inlet control device command.
By changing both the inlet and outlet control devices, it is possible to rapidly change engine torque and engine speed despite response delays of airflow inducted through the intake manifold. Since the cylinder air charge can be rapidly changed, the cylinder air/fuel ratio change can be compensated and abrupt changes in engine torque can be avoided. In other words, the present invention controls manifold inlet and outlet flows in a coordinated way to allow a rapid change in engine speed regardless of manifold volume. This rapid cylinder air charge change allows torque disturbances to by rapidly rejected without using an ignition timing torque reserve.
An advantage of the above aspect of the invention is that sustained torque disturbances can rejected.
Another advantage of the above aspect of the invention is that by using both an outlet and an inlet control device, a more controlled rapid change in engine torque and engine speed.
Other objects, features and advantages of the present invention will be readily appreciated by the reader of this specification.